Vocab 1

Question 1

The study of radiative transitions between the stationary energy states of an atom or molecule.

Answer 1

spectroscopy

Question 2

Particles of energy radiating from a source and characterized by an electromagnetic wave

Answer 2

photons

Question 3

The spatial period of an electromagnetic wave, i.e. the number of units of length per wave,
characterized in units of distance, e.g. Å, nm, μm, mm, cm, m, km, etc.

Answer 3

wavelength

Question 4

The number of waves per second, i.e. n in s-1. A quantity directly related to the energy
difference between two stationary energy states, e.g. ΔE = h ν .

Answer 4

frequency

Question 5

The spatial frequency of a wave, or number of waves per cm, equal to the reciprocal of its wavelength in cm. a term that describes the energy involved in an atomic or molecular transition, expressed in units of cm-1.

Answer 5

wavenumber

Question 6

The amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt; equivalent to 1.6021 ́ 10-^19 J.

Answer 6

electron volt

Question 7

The simplest wave form for which the profile is a sine or cosine curve with a specified frequency and period

Answer 7

harmonic wave

Question 8

graphical representation of an object moving with simple harmonic motion

Answer 8

circle of reference

Question 9

the amount of time it takes for one complete wave to pass a stationary point

Answer 9

period

Question 10

The scalar measure of rotation rate and is the magnitude of the vector quantity angular velocity, expressed in radians per second

Answer 10

angular frequency

Question 11

An angle measured relative to the x-axis of the circle of reference that specifies the displacement and direction of propagation of a wave.

Answer 11

phase angle

Question 12

The phase angle at t = 0.

Answer 12

initial phase angle

Question 13

Waves that oscillate perpendicularly to the direction of propagation, i.e.
electromagnetic waves.

Answer 13

transverse wave

Question 14

Waves that have the same direction of vibration as their direction of propagation, i.e. acoustic waves.

Answer 14

longitudinal wave

Question 15

When two or more waves traverse the same space, a disturbance occurs that is the sum of the disturbances caused by the individual waves; the resulting electromagnetic disturbance is the algebraic sum of the individual constituent waves.

Answer 15

principle of superposition

Question 16

The difference in the absolute phase angles of two electromagnetic waves, δ =φ2 −φ1 ; also defined as the amount by which one sin wave leads or lags another sin wave ; can be measured in degrees or radians.

Answer 16

Relative Phase Angle / Phase Shift / Phase Difference

Question 17

two electromagnetic waves for which the phase difference δ is zero

Answer 17

coherence

Question 18

The interaction of light waves to yield a resultant irradiance that is different from
the sum of the component waves

Answer 18

optical interference

Question 19

Two electromagnetic waves having a phase difference d of 0° or 360°, or an
integer multiple of 360°, occurs when δ = 0, ± 2π , ± 4π , etc. radians.

Answer 19

constructive interference

Question 20

Two electromagnetic waves having a phase difference d of 180° or 180° plus an
integer multiple of 360°

Answer 20

destructive interference

Question 21

The description of how any general function or periodic waveform can be
approximated by the summation of simpler sine and cosine terms.

Answer 21

fourier analysis

Question 22

stable provider of radiant energy

Answer 22

source

Question 23

Device that discriminates polychromatic source energy into individual wavelengths.

Answer 23

wavelength selector

Question 24

Device that converts radiant energy into an electrical signal, or other physical property, e.g. heat or resistance, that can be measured.

Answer 24

radiation detector

Question 25

A source of electromagnetic radiation whose spectral energy distribution is a function of both temperature and wavelength.

Answer 25

black-body radiator

Question 26

The flux of radiation in waveband d l escaping from a hole of unit area into a unit solid angle.

Answer 26

luminescence

Question 27

The cone generated by a line that passes through the vertex and a point moved along the periphery of the surface of the sphere; units = steradians (sr).

Answer 27

solid angle

Question 28

Relationship describing how the absolute intensity of the energy emitted from a black-body source increases, and the wavelength maximum of the distribution shifts, toward shorter wavelengths.

Answer 28

wien displacement law

Question 29

The ratio of the spectral radiance of a source to that of a black-body radiator at the same wavelength and T.

Answer 29

spectral emissivity

Question 30

A source whose spectral emissivity is less than one.

Answer 30

gray body

Question 31

An filter that uses the principles of optical interference to transmit a narrow band of measurement wavelengths. an optically resonant cavity formed by two partially reflecting mirrors that are non-absorbing and therefore transmit the light that is not reflected.

Answer 31

Fabry-Perot Filter

Question 32

substance that is a poor conductor of electricity, but that can be polarized by an applied electric field; a term that describes materials with a high polarizability, including many glasses and optical materials.

Answer 32

dielectric material

Question 33

A filter that transmits radiation with a certain range of wavelengths and attenuates or blocks wavelengths outside that range.

Answer 33

bandpass filter

Question 34

A filter that absorbs all radiation shorter than a given wavelength, and passes all radiation longer than this wavelength – also called a “long pass” filter.

Answer 34

Short-Wavelength Cut-Off Filter

Question 35

A filter that absorbs all radiation longer than a given Wavelength, and passes all radiation shorter than this Wavelength – also called a “short pass” filter.

Answer 35

Long-Wavelength Cut-Off Filter

Question 36

The variation of the index of refraction of a medium with the wavelength of the incident radiation

Answer 36

dispersion

Question 37

The ratio of the speed of an electromagnetic wave in a vacuum to its speed in an arbitrary medium other than vacuum

Answer 37

index of refraction

Question 38

The description of how a light ray changes direction at a single surface between two media with different refractive indicies

Answer 38

snells law

Question 39

The change in reflected angle with the change in wavelength

Answer 39

angular dispersion

Question 40

The linear separation of two wavelengths in the focal plane of a monochromator

Answer 40

linear dispersion

Question 41

The difference in the wavelengths of two lines divided by the observed separation of these lines in the focal plane of a monochromator

Answer 41

reciprocal linear dispersion

Question 42

The ability to separate adjacent absorption bands or spectral lines; the
smallest discernable difference in wavelength

Answer 42

resolution / resolving power

Question 43

The generally accepted criterion for determining whether two adjacent spectral lines are fully resolved; defined as the central maximum of the first spectral line falling on the first minimum of the second line; practically measured as a ~19% minimum between two equally intense lines.

Answer 43

rayleigh criterion

Question 44

The limiting case where light approaching the diffracting object is parallel and monochromatic, and where the image plane is at a distance large compared to the size of the diffracting object. consists of a central maximum peak with side peaks of gradually decreasing intensity.

Answer 44

Fraunhofer Diffraction

Question 45

plane surface consisting of a large number of very small, parallel, equally spaced grooves, at which different wavelengths constructively interfere at specific angles, leading to an angular dependence of intensity maxima, according to the grating equation

Answer 45

diffraction grating

Question 46

The integral multiples of the wavelength, m, that satisfies the grating equation and assumes the values 0, ±1, ±2, etc.

Answer 46

order of diffraction

Question 47

The density of grooves in the diffraction grating equation, d ; usually denoted in units of grooves mm-1.

Answer 47

groove spacing

Question 48

The multiple wavelengths l that satisfy the grating equation and appear at a given diffraction angle β for a given groove spacing d, and a given angle of incidence α

Answer 48

overlapping orders

Question 49

The range of wavelengths diffracting from the grating for which no overlap of adjacent orders occurs.

Answer 49

free spectral range

Question 50

A grating that has its groove facets titled at a particular angle with respect to the flat surface plane of the grating.

Answer 50

blazed grating

Question 51

The angle the grating groove facet is tilted with respect to the flat surface plane of the grating ; geometrically equivalent to the angle between the normal to the grating and the normal to the groove face.

Answer 51

blaze angle

Question 52

The first-order wavelength corresponding to the m = 1 diffracted radiation from a blazed grating.

Answer 52

blaze wavelength

Question 53

Very coarsely ruled (~100 grooves mm-1) gratings with very large blaze angles designed to be used in special monochromators with large diffraction angles and high orders to achieve high resolution.

Answer 53

echelle grating

Question 54

Widely used dispersive instrument used to optically isolate single wavelengths from a polychromatic source.

Answer 54

monochromator

Question 55

Dispersive instrument used to optically isolate multiple wavelengths simultaneously from a polychromatic source. implies multiple single element detectors located at multiple exit slits in the instrument

Answer 55

polychromator

Question 56

An instrument used for dispersing electromagnetic radiation from a polychromatic source into its component spectrum. Can also refer to a dispersive instrument, e.g. a Czerny-Turner monochromator, in which the single element detector at the exit slit is replaced by a multichannel detector that records large segments of the spectrum at once in the focal plane of the instrument.

Answer 56

spectrograph

Question 57

Common monochromator design in which a broad band illumination source is aimed at an entrance slit. The amount of light energy entering the monochromator is defined by the slit geometry and the acceptance angle of the optical system. The slit is placed at the effective focus of a curved collimating mirror so that the light from the slit reflected from the mirror is collimated. The collimated light is diffracted from the grating and then is collected by the final focusing mirror that refocuses the light, now dispersed, onto the exit slit.

Answer 57

Czerny-Turner monochromator

Question 58

The half-width of the wavelength distribution passed by the exit slit of a monochromator

Answer 58

effective bandwidth

Question 59

The angle φ that the diffracted ray makes with respect to the optic axis in a monochromator.

Answer 59

takeoff angle

Question 60

The angle θ that the grating makes with respect to the optic axis in a monochromator, as measured from the normal to the grating surface

Answer 60

grating rotation angle

Question 61

common mechanical drive mechanism for monochromators in which l is directed proportional to sin q , therefore the distance the lead screw is moved is directly proportional to wavelength

Answer 61

sine bar drive

Question 62

The convolution of the entrance and exit slit images resulting in the shape of the instrument profile in a dispersive grating monochromator.

Answer 62

slit function